Guest-Regulated Luminescence and Force-Stimuli Response of a Hydrogen-Bonded Organic Framework.

Guest molecules may endow porous materials with new or enhanced properties as well as functions. Here, a porous hydrogen-bonded organic framework (HOF) constructed from a three-armed triphenylamine derivative is used to investigate how guests regulate photoluminescence and trigger force-stimuli response. It was found that guest solvents in pores might regulate HOF's luminescence. Interestingly, acetic acid as a guest endowed HOF materials with longer emission wavelengths and triggered the responses to mechanical force stimuli. Under shear force, an obvious blueshift in emission spectra was observed because of the loss of free guests and the conversion of π-stacking model. Further blue-shifted emission appeared while the bound guests were completely removed by heating. Mechanofluorochromic HOF materials could be regenerated through recrystallization and adsorbing guest. Conversely, HOFs with other guests and activated HOFs only resulted in a slight change in their fluorescence behaviors after force stimuli.

Photo-oligomerization by shifting the coordination site in a luminescent coordination polymer.

A layered coordination polymer (CP) with the fine-tuned alignment of four diolefinic ligands has been designed by shifting the coordination site of the ligand. The trimeric and tetrameric cyclobutane derivatives were reversely achieved by the photoinitiated [2+2] cycloaddition of the CP due to the favorable Schmidt's distance. More interestingly, a dynamic fluorescence shift was observed during the photo-oligomerization and heat-cycloreversion of the CP system.

Hollow Zn-Co Based Zeolitic Imidazole Framework as a Robust Heterogeneous Catalyst for Enhanced CO2 Chemical Fixation.

The efficient chemical conversion of carbon dioxide (CO2 ) into value-added fine chemicals is an intriguing but challenging route in sustainable chemistry. Herein, a hollow-structured bimetallic zeolitic imidazole framework composed of Zn and Co as metal centers (H-ZnCo-ZIF) has been successfully prepared via a post-synthetic strategy based on controllable chemical-etching of the preformed solid ZnCo-ZIF in tannic acid. The creation of hollow cavities inside each monocrystalline ZIFs could be achieved without destroying the intrinsic frameworks, as characterized by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction technologies. The as-synthesized H-ZnCo-ZIF exhibited remarkable catalytic activity in the cycloaddition of CO2 with epoxides to the corresponding cyclic carbonates, outperforming the solid ZnCo-ZIF analogue due to the improved mass transfer originating from the hollow structure. More importantly, due to stabilization of metal centers in the ZIF framework by the tannic acid shell, H-ZnCo-ZIF exhibited good recyclability, and no activity loss could be observed in six runs. The present study provides a simple and effective strategy to enhance the catalytic performance of ZIFs by creating a hollow structure via chemical etching.

Co-ligand tuned pyrimidine-2-carboxylate Mn(ii) complexes from a 2D 63 layer to an interpenetrated srs-net.

A 63 2D layer complex [Mn3Cl3(L3)]n·H2O (1) (L = pyrimidine-2-carboxylate) was obtained by assembling 2-cyanopyrimidine and manganese chloride, in which the L ligands were generated in situ. In 1 six-membered Mn rings were constructed from MnII ions and L ligands, which were connected to each other by double chloride anions affording a 2D layer. When the chloride anions in 1 were substituted partly by formate, [Mn4Cl3L4(HCO2)]n (2) was obtained. In 2, the L ligands bridge MnII to give a 1D chain, which was further connected by the double chloride anions and Cl/formate bridges to form a two-fold interpenetrated srs-net. Interestingly, 2 exhibits an obvious SHG response of approximately 0.8 times that of KDP. Furthermore, 2 is an antiferromagnet with a field induced spin flop transition.

Why Porous Materials Have Selective Adsorptions: A Rational Aspect from Electrodynamics.

Gas storage/separation is a typical application of porous materials such as metal organic frameworks (MOFs). The adsorption/separation behavior results from the host-guest and/or guest-guest interaction and equilibration (host, porous material; guest, adsorbates). Although the driving forces for gas adsorption have been investigated, a detailed picture of interactions between gas molecules and MOFs has not clearly emerged. Herein, a new cobalt microporous MOF [Co(tipb)(adc)](DMF)3(H2O)1.5, which possesses a rare self-interpenetrated gra topology, has been prepared with both tipb and H2adc ligands (tipb = 1,3,5-tris(p-imidazolylphenyl)benzene, adc = 9,10-anthracenedicarboxylate). This MOF shows high stability and exceptional selective adsorption of CO2 over N2, O2, and CH4. In particular, a theoretical assumption of a "regional dynamic electric field effect" is proposed to clarify the selective adsorption. Moreover, we suggest that the proposed effect may be one of the most important factors impacting gas separation and storage in porous materials.

Light-triggered Supramolecular Isomerism in a Self-catenated Zn(II)-organic Framework: Dynamic Photo-switching CO2 Uptake and Detection of Nitroaromatics.

A self-catenated Zn(II)-organic framework formulated as [Zn2(3,3'-bpeab)(oba)2]·DMF (1) exhibiting a six-connected 44·610·8 topology has been successfully synthesized through the mixed-ligand of kinked 3,3'-bis[2-(4-pyridyl)ethenyl]azobenzene (3,3'-bpeab) and 4,4'-oxybis-benzoic acid (H2oba) under solvothermal condition. UV light triggers isomerization of complex 1 in a single-crystal-to-single-crystal (SCSC) manner, giving rise to a conformational supramolecular isomer 1_UV through the pedal motion of photoresponsive double bonds. Dynamic photo-switching in the obtained light-responsive supramolecular isomers leads to instantly reversible CO2 uptake. Furthermore, the ligand originated fluorescence emission of water-resistant complex 1 is selectively sensitive to 4-nitrotoluene (4-NT) owing to a higher quenching efficiency of the perilous explosive over other structurally similar nitroaromatics, prefiguring the potentials of 1 as a fluorescence sensor towards 4-NT in aquatic media.

Crystal engineering to control the magnetic interaction between weak ferromagnetic single-chain magnets assembled in a 3D framework.

A new single-chain-magnet (SCM), [Co4(OMe)3(HCO2)2(L)3·DMF]n, (L = 4-(pyridin-4-yl)benzolate) (2), was constructed by changing the spacers of a weak ferromagnetic single-chain magnet [Co8(OMe)6(HCO2)4(isonic)6·H2O]n (1). By contrasting the magnetism of the two complexes, it is found that the longer the linker the stronger the magnetic properties.

4-Substituent pyridine directed cobalt(II) azides: solvothermal synthesis, structure, and magnetic properties.

The structure and magnetism of three cobalt(ii)-azide complexes, [Co(N3)2(bepy)2]n (), [Co2(N3)4(vipy)4]n (), and [Co(N3)2(bipy)]n () were tuned by three structurally related 4-substituent pyridines, 4-benzylpyridine (bepy), 4-vinyl pyridine (vipy), and 4,4'-bipyridine (bipy) as co-ligands in solvothermal reactions. With flexible benzyl as a substituent group of the pyridine co-ligand, a one-dimensional (1D) complex with double end-to-end (EE) azide-bridging Co(ii) chain is formed. While using a rigid but small vinyl group as the substituent, a distinct Co(ii)-azide chain with alternate double end-on (EO) and double EE azide bridges was obtained. Finally, when another pyridine group was used instead of the substituent incapable of coordinating in and , a bipyridine, it gave rise to a chiral complex with a three-dimensional (3D) diamondoid Co(ii)-azide framework further reinforced by the bipy ligand. Magnetic studies indicate antiferromagnetic interactions between the Co(ii) ions in the three complexes, but interestingly, weak antiferromagnetism origin of spin canting exists in at low temperatures.

Ratiometric fluorescence detection of fluoride ion by indole-based receptor.

A novel artificial receptor 1 containing the indolocarbazole-NH moieties as the recognition sites exhibited high selectivity and sensitivity toward F(-) over other typical anionic species in DMSO solution. Upon addition of F(-) into the solution, receptor 1 showed a remarkable ratiometric shift of the fluorescence maximum from 535 to 590 nm, and also a prominent color change from light yellow to orange, which was observable by the naked eye. The recognition properties of receptor 1 were investigated by (1)H NMR, UV-vis, and fluorescence titration experiments, with the results suggesting a two-step strategy of binding with F(-). In addition, the theoretical calculations were carried out to reveal the role of intramolecular charge transfer in the ratiometric fluorescence recognition process.

A controllable gate effect in cobalt(II) organic frameworks by reversible structure transformations.

With H2 O or NH3 stimuli, the blue cobalt-based metal-organic framework (MOF) BP can reversibly transform to red RP. The removal/recovery of terephthalate ligands accompanied by the transformation leads to a gate effect, which allows the encapsulation and release of small solvent molecules under certain conditions. This is the first example of topology transformation from a self-penetrating to interpenetrating net in 3D MOFs.

Slow magnetic relaxation in two new 1D/0D Dy(III) complexes with a sterically hindered carboxylate ligand.

Two carboxylate-bridged Dy(III) complexes, [Dy(2)(piv)(5)(µ(3)-OH)(H(2)O)](n) (1) and [Dy(2)(piv)(6)(phen)(2)] (2) (pivH = pivalic acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized. Complex 1 takes a one-dimensional (1D) chain structure based on [Dy(4)(µ(3)-OH)(2)(piv)(8)(H(2)O)(2)](2+) units, while complex 2 is a dinuclear structure bridged by syn,syn-carboxylates. Magnetic investigation indicates weak ferromagnetic interaction between adjacent Dy(III) ions of the Dy(4) unit in 1 and weak intramolecular antiferromagnetic interaction between Dy(III) ions and/or depopulation of the Dy(III) excited-state Stark sublevels in 2. Alternating-current susceptibility measurements revealed frequency- and temperature-dependent out-of-phase signals under a zero direct-current field in 1, with typical slow magnetic relaxation behavior with an anisotropic barrier U ≈ 4.5 K, while 2 exhibits field-induced single-molecule-magnet behavior with ΔE/k(B) = 28.43 K under a 2 kOe external field.

Synthesis and ferrimagnetic properties of an unprecedented polynuclear cobalt complex composed of [Co24] macrocycles.

An unprecedented polynuclear cobalt complex with a [Co(24)] macrocycle in the presence of [Co(H(2)O)(6)](2+) has been prepared and characterized. In this complex, [Co(H(2)O)(6)](2+) not only acts as a counterion to balance the negative charge of the 2D layer, but may also serve as a template in the assembly of the [Co(24)] macrocyclic complex through hydrogen-bond interactions. Magnetic analyses indicate that the title compound shows homometallic ferrimagnetic behavior.

Ratiometric and selective fluorescent sensor for Zn2+ as an "off-on-off" switch and logic gate.

A new chemosensor, 2,3,15,16-tetrakis(pyridin-2-yl)-7,8,10,11,20,21,23,24-octahydro[1,4,7,10,13,16]hexaoxacyclooctadecino[2,3-g:11,12-g']diquinoxaline (1), containing 2,3-bis(pyridin-2-yl)quinoxaline and crown ether moieties, has been designed and found to be a ratiometric and selective fluorescent detector of Zn(2+) over a wide range of tested metal ions. The addition of Zn(2+) to the solution of 1 in acetonitrile induced the formation of a 1:2 ligand-metal complex, 1-Zn(2+), which exhibits a remarkable enhanced fluorescent emission centered at 460 nm, with the disappearance of the fluorescent emission of 1 centered at 396 nm due to the mechanism of internal charge transfer. In contrast, the presence of K(+) results in the fluorescence quenching of 1 and 1-Zn(2+) through the photoinduced electron-transfer mechanism. These results demonstrate that 1 can perform as not only an INHIBIT logic gate but also an "off-on-off" molecular switch triggered by Zn(2+) and K(+). The structure of complex 1-Zn(2+) has been characterized by single-crystal X-ray crystallography, mass spectrometry, and (1)H NMR titration experiments. Density functional theory calculation results on 1 and the 1-Zn(2+) complex are well consistent with the experimental results.

A new ion pair receptor fulfilling a dual function as a chromogenic molecular switch for F- and ratiometric selective recognition of HSO4(-).

A new ditopic ion pair receptor 1 containing two biindole moieties and a bis-benzocrown ether unit shows a remarkable color switching (ON- and -OFF) function induced by anion (F(-)) and cation (K(+)) recognition. The ditopic receptor 1 binds in a cooperative fashion to HSO(4)(-) in the presence of 1·K(+) and acts as a selective ditopic receptor to recognize ion pairs with a wavelength-ratiometric manner.

Two azido-bridged cobalt(II) coordination polymers with nicotinate co-ligand: synthesis, structures and magnetic properties.

By utilizing nicotinic acid as a co-ligand, two new azido-bridged cobalt(II) complexes with the formulae [Co(2)(N(3))(nic)(2)Cl(H(2)O)](n) (1) and [Co(N(3))(nic)](n) (2) (nic = nicotinate) have been synthesized under solvothermal condition and structurally characterized. Complex 1 exhibits a rare three-dimensional (3D) Kagomé topology with [Co4] units as connecting nodes. Complex 2 is also a 3D structure which contains 1D Co(II)-µ-1,1-azido chains as rod-shaped SBUs. Magnetic data analysis shows that ferromagnetic coupling intra-[Co4]-cluster and antiferromagnetic interaction inter-[Co4]-cluster exists in complex 1, while complex 2 exhibits metamagnetism with a critical field of 5.5 kOe.

Valence-induced assembly of Cu(I)-Cu(II) ions into different discrete coordination architectures by a disk-shaped polypyridyl ligand.

The valences of metal ions were found to play key roles in controlling the formation and structures of discrete coordination architectures in a copper and disk-shaped hexa-monodentate ligand system. When Cu(I) and Cu(II) ions react with a polydentate ligand HPDQ, a hexanuclear "double-decker" like discrete "LM(3)M(3)L" coordination architecture (CuI)(6)(HPDQ)(2)(CHCl(3))(8) (complex 1), and a "LM(3)L + LM(3)" composite structure complex (Cu(NO(3))(2))(6)(HPDQ)(3) (complex 2) are formed, respectively.

One pot synthesis of heterometallic 3d-3d azido architectures: assembling strategy and magnetic properties.

The Cu(II) ions usually have different coordinated geometry to other 3d ions, especially Ni(II) and Co(II) ions, in azido-carboxylate mixed ligand systems. That provides a potential way to synthesize rare heterometallic 3d-3d azido complexes with peculiar magnetic properties. Assembling Cu(II), M(II) (M = Ni and Co), azido and nicotinic acid in hydrothermal condition, two novel isomorphic 3D heterometallic 3d-3d azido complexes, [CuM(N(3))(2)(nicotinate)(2)](∞) (M = Ni(II) for 1 and Co(II) for 2) were obtained. The structure of the complexes can be described as EO azido and syn,syn carboxylate mixed bridged spin sequence chains (-1/2-J(1)-1-J(2)-1/2- for 1 and -1/2-J(1)-3/2-J(2)-1/2- for 2) linked by the pyridyl groups. Dominant ferromagnetic interactions were observed between the Cu(II) and M(II) ions in the chains despite the largest M-N-M angle of about 129° in the 3d metal azido-carboxylate mixed coordinated systems and weak antiferromagnetic interactions between the chains. At low temperature, a spin-flop phase transition was present in the Co(II) involved complex 2.

Zn(II) and Cd(II) coordination polymers assembled by di(1H-imidazol-1-yl)methane and carboxylic acid ligands.

Five new Zn(II)/Cd(II) coordination polymers constructed from di(1H-imidazol-1-yl)methane (L) mixed with different auxiliary carboxylic acid ligands formulated as [Zn(L)(H(2)L(1))(2)·(H(2)O)(0.2)](n) (1), {[Zn(L)(L(2))]·H(2)O}(n) (2), {[Cd(2)(L)(2)(L(2))(2)]·2H(2)O}(n) (3), {[Cd(L)(L(3))]·H(2)O}(n) (4) and [Cd(L)(L(4))](n) (5) (H(3)L(1) = 1,3,5-benzenetricarboxylic acid, H(2)L(2) = 4,4'-oxybis(benzoic acid), H(2)L(3) = m-phthalic acid and H(2)L(4) = p-phthalic acid) have been synthesized under hydrothermal conditions and structurally characterized. Four related auxiliary carboxylic acids were chosen to examine the influences on the construction of these coordination frameworks with distinct dimensionality and connectivity. The coordination arrays of 1-5 vary from 1D zigzag chain for 1, 2D (4,4) layer for 2-4, to 2-fold interpenetrated 3D coordination network with the α-Po topology for 5. The thermal and photoluminescence properties of complexes 1-5 in the solid state have also been investigated.

Isomorphous tetrazolate MnII and CoII compounds built on Δ-chain showing different magnetic behaviors.

As a continuation of the study on using the tetrazolate ligands to construct coordination polymers, two isomorphous 3D coordination polymers built on Δ-chain topological rod-shaped SBUs have been synthesized with formulae [M(2)(µ(3)-OH)L(1)L(2)](n) (5-amino-1H-tetrazole (HL(1)), 2,3-pyrazinedicarboxylic acid (H(2)L(2)) and different 3d spin carriers (M = Mn(II), 1 and Co(II), 2)). The SBU consists of corner-sharing [M(3)(µ(3)-OH)] isosceles triangle motifs with mixed multiple (µ(4)-tetrazolyl, µ(3)-OH, syn-syn carboxylate) bridges. The SBUs were further linked by syn-anti carboxylates to form the sra net. Spin-competing was observed in the Mn(II) compound, whereas the Co(II) compound exhibits spin-canting.